TSEARCH(3) Linux Programmer's Manual TSEARCH(3)
NAME
tsearch, tfind, tdelete, twalk - manage a binary tree
SYNOPSIS#include<search.h>void*tsearch(constvoid*key,void**rootp,int(*compar)(constvoid*,constvoid*));void*tfind(constvoid*key,constvoid**rootp,int(*compar)(constvoid*,constvoid*));void*tdelete(constvoid*key,void**rootp,int(*compar)(constvoid*,constvoid*));voidtwalk(constvoid*root,void(*action)(constvoid*nodep,constVISITwhich,constintdepth));DESCRIPTIONtsearch, tfind, twalk, and tdelete manage a binary tree.
They are generalized from Knuth (6.2.2) Algorithm T. The
first field in each node of the tree is a pointer to the
corresponding data item. (The calling program must store
the actual data.) compar points to a comparison routine,
which takes pointers to two items. It should return an
integer which is negative, zero, or positive, depending on
whether the first item is less than, equal to, or greater
than the second.
tsearch searches the tree for an item. key points to the
item to be searched for. rootp points to a variable which
points to the root of the tree. If the tree is empty,
then the variable that rootp points to should be set to
NULL. If the item is found in the tree, then tsearch
returns a pointer to it. If it is not found, then tsearch
adds it, and returns a pointer to the newly added item.
tfind is like tsearch, except that if the item is not
found, then tfind returns NULL.
tdelete deletes an item from the tree. Its arguments are
the same as for tsearch.
twalk performs depth-first, left-to-right traversal of a
binary tree. root points to the starting node for the
traversal. If that node is not the root, then only part
of the tree will be visited. twalk calls the user func-
tion action each time a node is visited (that is, three
times for an internal node, and once for a leaf). action,
in turn, takes three arguments. The first is a pointer to
the node being visited. The second is an integer which
takes on the values preorder, postorder, and endorder
depending on whether this is the first, second, or third
visit to the internal node, or leaf if it is the single
visit to a leaf node. (These symbols are defined in
<search.h>.) The third argument is the depth of the node,
with zero being the root.
RETURNVALUEtsearch returns a pointer to a matching item in the tree,
or to the newly added item, or NULL if there was insuffi-
cient memory to add the item. tfind returns a pointer to
the item, or NULL if no match is found. If there are mul-
tiple elements that match the key, the element returned is
unspecified.
tdelete returns a pointer to the parent of the item
deleted, or NULL if the item was not found.
tsearch, tfind, and tdelete also return NULL if rootp was
NULL on entry.
WARNINGStwalk takes a pointer to the root, while the other func-
tions take a pointer to a variable which points to the
root.
twalk uses postorder to mean "after the left subtree, but
before the right subtree". Some authorities would call
this "inorder", and reserve "postorder" to mean "after
both subtrees".
tdelete frees the memory required for the node in the
tree. The user is responsible for freeing the memory for
the corresponding data.
The example program depends on the fact that twalk makes
no further reference to a node after calling the user
function with argument "endorder" or "leaf". This works
with the GNU library implementation, but is not in the
SysV documentation.
EXAMPLE
The following program inserts twelve random numbers into a
binary tree, then prints the numbers in order. The num-
bers are removed from the tree and their storage freed
during the traversal.
#include <search.h>
#include <stdlib.h>
#include <stdio.h>
void *root=NULL;
void *xmalloc(unsigned n)
{
void *p;
p = malloc(n);
if(p) return p;
fprintf(stderr, "insufficient memory\n");
exit(1);
}
int compare(const void *pa, const void *pb)
{
if(*(int *)pa < *(int *)pb) return -1;
if(*(int *)pa > *(int *)pb) return 1;
return 0;
}
void action(const void *nodep, const VISIT which, const int depth)
{
int *datap;
void *val;
switch(which)
{
case preorder:
break;
case postorder:
datap = *(int **)nodep;
printf("%6d\n", *datap);
break;
case endorder:
datap = *(int **)nodep;
(void)tdelete(datap, &root, compare);
free(datap);
break;
case leaf:
datap = *(int **)nodep;
printf("%6d\n", *datap);
val = tdelete(datap, &root, compare);
free(datap);
break;
}
return;
}
int main()
{
int i, *ptr;
void *val;
for (i = 0; i < 12; i++)
{
ptr = (int *)xmalloc(sizeof(int));
*ptr = rand()&0xff;
val = tsearch((void *)ptr, &root, compare);
if(val == NULL) exit(1);
}
twalk(root, action);
return 0;
}
CONFORMINGTO
SVID
SEEALSOqsort(3), bsearch(3), hsearch(3), lsearch(3)
GNU September 24, 1995 1